Dose-dependency of intra-articular morphine analgesia

We have examined if the analgesic effects of intra-articular morphine are dose-dependent in patients undergoing elective arthroscopic knee surgery. At the end of surgery, patients were allocated randomly to one of four groups to receive intra-articular saline (n = 22), or morphine 1 mg (n = 24), 2 mg (n = 21) or 4 mg (n = 19). After operation, patients remained in hospital overnight and pain intensity was assessed using a visual analogue scale at 1, 2, 3, 6, 9, 12, 18 and 24 h after intra-articular injection. Patients requesting additional analgesia received a loading dose of piritramide 0.1 mg kg-1 i.v. and were connected to a PCA device using the same drug. Increasing doses of intra-articular morphine were associated with greater analgesic effects and less supplementary analgesic requirements.